Various types of drilling tools are known which are adapted to ream a hole of a desired diameter while cutting the wall of the hole. Such drilling tools are a single-purposed, exclusive and/or automated tool which can be increased in cutting efficiency and used to provide high-quality and uniform products.
Japanese Utility Model Application laid open under Kokai publication No. 62-65107 discloses a reamer section drill including two drilling edges and four reaming edges, all these edges being arranged in the same circle.
FIGS. 11 and 12 in the accompanying drawings show another burnishing drill. Such a burnishing drill comprises a cylindrical drill body 2 connected with a shank 1, the drill body 2 includes cutting edges 5, formed therein, at the tip 3 thereof, and opposed to each other diametrically about the longitudinal axis of the drill body 2. Each of the cutting edges 5 includes a slant face 6 extending therefrom rearwardly in the direction of rotation (indicated by arrow A in FIG. 12) and a guide face 7 axially extending from the edge of the slant face 6. The drill body 2 further includes a longitudinally extending relief surface 8 formed therein between each of the cutting edges 5 and the corresponding guide face 7 at the outer wall of the drill body 2 and a longitudinally extending relief groove 9 formed in the drill body 2.
This drill does not have good centering and stabilizing properties since the initial bite cannot be properly made. As a result, the drilled hole made is excessively reamed and its inner wall is rough. This drill often generates a built-up edge.